1. Field of the Invention
The present invention relates to a method for measuring receive sensitivity of a base station having multiple frequency allocations (FAs), and more particularly to a method for measuring receive sensitivity of a base station in order to test a plurality of FAs with only one test terminal.
2. Description of the Prior Art
In general, CDMA (code division multiple access) refers to a kind of multiple access method, which allows a plurality of users to communicate at the same time and/or frequency in a wireless communication system employed in car phones, cellular (or portable) phones and so forth.
The CDMA system is a spread spectrum communication system, in which information signals are transmitted in a state, in which, the information signals are subjected to spreading at a wider bandwidth than that of the original information signals. Further, when original data are transmitted, they are subjected to spreading by means of PN (pseudo random noise) codes called spreading codes. Then, when the spread data are received, they are subjected to de-spreading by means of the same PN codes as the PN codes which are used to transmit the data, so that the received data are regenerated into the original data. In this CDMA system, there may be caused a near-far problem in which communication of a transmitting station is disturbed by a signal from another transmitting station (which functions as an interference station) in a case where the interference station is located much nearer than the transmitting station from the targeted station (base station). Consequently, the more distant desired mobile station has difficulty in performing communication due to such interference. In order to solve the near-far problem, it is necessary to precisely control the transmission power in such a manner that the less distant mobile station uses a lower transmission power while the more distant mobile station uses a higher transmission power in transmitting a signal.
FIG. 1 is a view illustrating a general communication between a CDMA base station and a mobile station, wherein the transmission route from the base station 10 to the mobile station 20 is a forward link (downlink) and the transmission route from the mobile station 20 to the base station 10 is a reverse link (uplink).
The power control of the reverse link in the CDMA system has been regarded as a very important factor because the power directly affects the acceptable number of subscriber and available communication distance. In a conversation phase, the base station 10 checks the sensitivity of the signals received from the mobile station (that is, a terminal) 20, and transmits a power control signal which causes the mobile station 20 to control the transmission power so that the base station 10 can receive the lowest power necessary for keeping a preset sensitivity for receiving signals. By the power control function, the input end of the base station 10 can receive the lowest power needed for demodulating the received signals, wherein the value of the lowest power is a receive sensitivity of the base station 10.
Meanwhile, the base station 10 may increase the capacity for subscribers by separating a service cell into several sectors with omni-directional antennas or multidirectional sector antennas.
FIG. 2 is a view illustrating an example of separating a service cell into three sectors, wherein the base station in the service cell provides communication service to each of the three sectors separated by three antennas 15-1 to 15-3. Then, the base station accommodates at least one FA (frequency allocation) per sector and provides transmitting/receiving functions to each sector independently.
In the CDMA base station, the transmission characteristic can be easily analyzed by using a conventional measuring instrument, while the analysis of the receiving characteristic must follow a very complicated process.
FIG. 3 is a schematic view illustrating an example of a conventional test construction for measuring the receive sensitivity of the CDMA base station.
Generally, a CDMA base station, not herein illustrated, comprises a control section, a network matching section, a time/frequency device, a digital signal process device and a RF signal device. The control section operates and manages the whole base station. The network matching section performs a packet routing function between the base station and a BSC (Base Station Controller) through E1 carrier system or T1 carrier system, and interfaces packet data among processors in the base station. The time/frequency device generates a reference frequency and a timing synchronization signal in order to synchronize processors in the base station and to perform a timing synchronization with neighbor base stations. The digital signal process device modulates/demodulates data and voice signals transmitted/received through the CDMA channel. The RF signal device converts high frequency radio signals received from a mobile station to IF (intermediate frequency) signals, and converts IF signals to high frequency radio signals.
In such a base station, a test system for the receive sensitivity, as shown in FIG. 3, includes a test terminal (mobile terminal) 31 connected to the high frequency radio end part of a base station 10 through a directional coupler 36 and cables, wherein the base station 10 comprises a high power amplifier (HPA) 11, a duplexer 12, a low noise amplifier (LNA) 13 and an antenna. Then, the test terminal 31, set in an electromagnetic wave blocking case, stores an original number for a subscriber, radio signals outputted from the test terminal 31 are transmitted to the directional coupler 36 through a coupler 32, a fist attenuator 33 and cables. Also, radio signals outputted from the test terminal 31 branch off through the coupler 32 and are transmitted to a spectrum analyzer 35 through a second attenuator 34 and cables. Thus, it is possible to analyze the receiving characteristic of the input end of the base station 10 by analyzing the signal level inputted into the spectrum analyzer 35. Specifically, two attenuation levels, which include one attenuation level from the test terminal 31 to the input end of the base station 10 through the first attenuator 33 and the directional coupler 36 and, the other attenuation level from the test terminal 31 to spectrum analyzer 35 through the second attenuator 34, can be measured. Therefore, the value of the signal level received in the input end of the base station 10 through the directional coupler 36 can be indirectly calculated by measuring the level of the test terminal 31 by using the spectrum analyzer 35. Conventionally, the receiving characteristic is measured after setting the attenuation value of the attenuator so as to adjust the level of the input end of the base station 10 to about −116 dBm.
A mobile station, belonging to a base station which has multi-FA (frequency allocation), determines its own FA frequency and performs synchronization according to the Hash Function by using its mobile identification number (MIN) with reference to CDMA standards. Thus, all mobile stations belonging to a base station having multi-FA always perform synchronization only to a special FA frequency channel by their mobile identification numbers (MINs).
Therefore, in order to measure the receive sensitivity of the base station having multi-FA, a plurality of terminals having different mobile identification numbers (MINs) from one another corresponding to the number of the FA are needed. Also, another problem includes that when the frequency channel is increased a complicated process must be followed, that is, the base station 10 must again allocate mobile identification numbers (MINs) in order to uniformly insure the frequency of the preset MINs for mobile stations already being operated as well as the frequency of the MINs for mobile stations being added.